U.S. patent application number 12/205117 was filed with the patent office on 2009-03-19 for imaging apparatus and focusing control method.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Masaaki Uenishi.
Application Number | 20090074392 12/205117 |
Document ID | / |
Family ID | 40454563 |
Filed Date | 2009-03-19 |
United States Patent
Application |
20090074392 |
Kind Code |
A1 |
Uenishi; Masaaki |
March 19, 2009 |
IMAGING APPARATUS AND FOCUSING CONTROL METHOD
Abstract
An imaging apparatus sets a main area and a plurality of
subareas around the main area in an image obtained from an image
sensor, and acquires each focusing state and each in-focus point
based on the each focusing state of the main area and the plurality
of subareas in an image obtained from the image sensor at each of a
plurality of focus lens positions while moving a focus lens. If the
focusing state of the main area does not satisfy a predetermined
condition, the imaging apparatus performs focusing control using
the focusing state of the main area and a focusing state of a
subarea having an in-focus point located within a predetermined
range from the in-focus point of the main area among the plurality
of subareas.
Inventors: |
Uenishi; Masaaki;
(Kawasaki-shi, JP) |
Correspondence
Address: |
CANON U.S.A. INC. INTELLECTUAL PROPERTY DIVISION
15975 ALTON PARKWAY
IRVINE
CA
92618-3731
US
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
40454563 |
Appl. No.: |
12/205117 |
Filed: |
September 5, 2008 |
Current U.S.
Class: |
396/104 |
Current CPC
Class: |
H04N 5/232945 20180801;
G03B 13/36 20130101; H04N 5/232123 20180801; H04N 5/232127
20180801; H04N 5/23212 20130101; G02B 7/08 20130101 |
Class at
Publication: |
396/104 |
International
Class: |
G03B 13/32 20060101
G03B013/32 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 14, 2007 |
JP |
2007-240183 |
Claims
1. An imaging apparatus comprising: a setting unit configured to
set a main area and a plurality of subareas around the main area in
an image obtained from an imaging unit; an acquisition unit
configured to acquire each focusing state and each in-focus point
based on the each focusing state of the main area and the plurality
of subareas in an image obtained from an imaging unit at each of a
plurality of focus lens positions while moving a focus lens; a
determination unit configured to determine whether the focusing
state of the main area satisfies a predetermined condition; and a
focusing control unit configured to, if it is determined by the
determination unit that the focusing state of the main area does
not satisfy the predetermined condition, perform focusing control
using the focusing state of the main area and a focusing state of a
subarea having an in-focus point located within a predetermined
range from the in-focus point of the main area among the plurality
of subareas.
2. The imaging apparatus according to claim 1, wherein the focusing
control unit is configured to perform focusing control based on a
combined focusing state obtained by combining the focusing state of
the main area with the focusing state of the subarea having an
in-focus point located within the predetermined range from the
in-focus point of the main area.
3. The imaging apparatus according to claim 2, wherein the
determination unit is configured to determine whether the combined
focusing state satisfies the predetermined condition, and wherein
the focusing control unit is configured to perform focusing control
based on the combined focusing state if the combined focusing state
satisfies the predetermined condition.
4. An imaging apparatus comprising: a setting unit configured to
set a main area and a subarea internally including the main area in
an image obtained from an imaging unit; an acquisition unit
configured to acquire each focusing state and each in-focus point
based on the each focusing state of the main area and the subarea
in an image obtained from the imaging unit at each of a plurality
of focus lens positions while moving a focus lens; a determination
unit configured to determine whether the focusing state of the
subarea satisfies a predetermined condition if the focusing state
of the main area does not satisfy the predetermined condition; and
a focusing control unit configured to, if it is determined by the
determination unit that the focusing state of the subarea satisfies
the predetermined condition and the in-focus points of the main
area and the subarea are located within a predetermined range,
perform focusing control using the focusing states of the main area
and the subarea.
5. The imaging apparatus according to claim 1, wherein the focusing
control unit is configured to drive the focus lens to the in-focus
point of the main area if it is determined that the focusing state
of the main area satisfies the predetermined condition.
6. The imaging apparatus according to claim 1, wherein the main
area includes an arbitrarily set area.
7. The imaging apparatus according to claim 1, further comprising a
detection unit configured to detect an object satisfying a
predetermined condition from an image obtained from the imaging
unit, wherein the detection unit is configured to set an area
including the object detected by the detection unit as the main
area.
8. The imaging apparatus according to claim 7, wherein the object
includes a face of human being.
9. A focusing control method comprising: setting a main area and a
plurality of subareas around the main area in an image obtained
from an imaging unit; acquiring each focusing state and each
in-focus point based on the each focusing state of the main area
and the plurality of subareas in an image obtained from the imaging
unit at each of a plurality of focus lens positions while moving a
focus lens; determining whether the focusing state of the main area
satisfies a predetermined condition; and if it is determined that
the focusing state of the main area does not satisfy the
predetermined condition, performing focusing control using the
focusing state of the main area and a focusing state of a subarea
having a in-focus point located within a predetermined range from
the in-focus point of the main area among the plurality of
subareas.
10. A focusing control method comprising: setting a main area and a
subarea internally including the main area in an image obtained
from an imaging unit; acquiring each focusing state and each
in-focus point based on the each focusing state of the main area
and the subarea in an image obtained from the imaging unit at each
of a plurality of focus lens positions while moving a focus lens;
determining whether the focusing state of the subarea satisfies a
predetermined condition if the focusing state of the main area does
not satisfy the predetermined condition; and if it is determined
that the focusing state of the subarea satisfies the predetermined
condition and the in-focus points of the main area and the subarea
are located within a predetermined range, performing focusing
control using the focusing states of the main area and the subarea.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an imaging apparatus and a
focusing control method. More particularly, the present invention
relates to an imaging apparatus, e.g., an electronic still camera
and a video camera, and a focusing control method utilized for the
imaging apparatus.
[0003] 2. Description of the Related Art
[0004] A conventional method to focus on an object in an imaging
apparatus, such as an electronic still camera, includes an
autofocus system which automatically moves the position of a focus
lens using a luminance signal obtained from an image sensor, such
as a charge-coupled device (CCD), so as to perform a focusing
operation. A general automatic focusing apparatus using the
autofocus system calculates an in-focus point by detecting a
position of a focus lens enabling the highest contrast based on a
focus evaluation value obtained by integrating high-frequency
components of a signal in a focus adjustment area set in a pixel
area of the image sensor.
[0005] However, the automatic focusing apparatus has problems, when
illuminance of an object is low or the amount of a high-frequency
component is small due to low contrast of an object, that a focus
evaluation value becomes low. Further, the ratio of noise
components included in a luminance signal becomes high, so that
focusing accuracy decreases.
[0006] In order to solve the above-described problem, Japanese
Patent Application Laid-Open No. 11-215426 discusses an autofocus
apparatus which expands a focus adjustment area when the
illuminance of an object is lower than a predetermined value, thus
improving signal to noise (S/N) ratio and improving focusing
accuracy at low illuminance.
[0007] Japanese Patent Application Laid-Open No. 2000-307392
discusses an autofocus apparatus which acquires focus evaluation
values in a plurality of focus adjustment areas and performs the
following control when a peak of a sufficient focus evaluation
value is not obtained in each focus adjustment area. That is, if
there is a plurality of focus adjustment areas having similar peak
positions of focus evaluation values, the autofocus apparatus
selects these focus adjustment areas, calculates an average
position of the peak positions in respective focus adjustment
areas, and sets the calculated average position as an in-focus
position. Thus, the autofocus apparatus can improve reliability of
a focus evaluation value peak at low illuminance.
[0008] However, when the autofocus apparatus expands a focus
adjustment area as discussed in Japanese Patent Application
Laid-Open No. 11-215426, an object other than a main object, e.g.,
a background, may enter the focus adjustment area, and thus the
apparatus may focus on an object other than a main object.
[0009] Furthermore, when a focus adjustment area having a similar
peak position of selected focus evaluation value is a focus
adjustment area including an object other than a main object, as
discussed in Japanese Patent Application Laid-Open No. 2000-307392,
the apparatus cannot select a frame including the main object and,
thus, cannot focus on the main object. Further, when an average
position of peak positions in a plurality of focus adjustment areas
is calculated, the apparatus cannot cancel randomly generated
noises and, thus, cannot improve S/N ratio.
SUMMARY OF THE INVENTION
[0010] The present invention is directed to improving focusing
accuracy for a main object when reliability of a focusing result in
a main focus adjustment area is low due to low illuminance or low
contrast of a main object.
[0011] According to an aspect of the present invention, an imaging
apparatus includes a setting unit configured to set a main area and
a plurality of subareas around the main area in an image obtained
from an imaging unit, an acquisition unit configured to acquire
each focusing state and each in-focus point based on the each
focusing state of the main area and the plurality of subareas in an
image obtained from the imaging unit at each of a plurality of
focus lens positions while moving a focus lens, a determination
unit configured to determine whether the focusing state of the main
area satisfies a predetermined condition, and a focusing control
unit configured to, if it is determined by the determination unit
that the focusing state of the main area does not satisfy the
predetermined condition, perform focusing control using the
focusing state of the main area and a focusing state of a subarea
having an in-focus point located within a predetermined range from
the in-focus point of the main area among the plurality of
subareas.
[0012] According to another aspect of the present invention, a
focusing control method includes setting a main area and a
plurality of subareas around the main area in an image obtained
from an imaging unit, acquiring each focusing state and each
in-focus point based on the each focusing state of the main area
and the plurality of subareas in an image obtained from the imaging
unit at each of a plurality of focus lens positions while moving a
focus lens, determining whether the focusing state of the main area
satisfies a predetermined condition, and, if it is determined that
the focusing state of the main area does not satisfy the
predetermined condition, performing focusing control using the
focusing state of the main area and a focusing state of a subarea
having an in-focus point located within a predetermined range from
the in-focus point of the main area among the plurality of
subareas.
[0013] According to yet another aspect of the present invention, an
imaging apparatus includes a setting unit configured to set a main
area and a subarea internally including the main area in an image
obtained from an imaging unit, an acquisition unit configured to
acquire each focusing state and each in-focus point based on the
each focusing state of the main area and the subarea in an image
obtained from the imaging unit at each of a plurality of focus lens
positions while moving a focus lens, a determination unit
configured to determine whether the focusing state of the subarea
satisfies a predetermined condition if the focusing state of the
main area does not satisfy the predetermined condition, and a
focusing control unit configured to, if it is determined by the
determination unit that the focusing state of the subarea satisfies
the predetermined condition and the in-focus points of the main
area and the subarea are located within a predetermined range,
perform focusing control using the focusing states of the main area
and the subarea.
[0014] According to yet another aspect of the present invention, a
focusing control method includes setting a main area and a subarea
internally including the main area in an image obtained from an
imaging unit, acquiring each focusing state and each in-focus point
based on the each focusing state of the main area and the subarea
in an image obtained from the imaging unit at each of a plurality
of focus lens positions while moving a focus lens, determining
whether the focusing state of the subarea satisfies a predetermined
condition if the focusing state of the main area does not satisfy
the predetermined condition, and, if it is determined that the
focusing state of the subarea satisfies the predetermined condition
and the in-focus points of the main area and the subarea are
located within a predetermined range, performing focusing control
using the focusing states of the main area and the subarea.
[0015] Exemplary embodiments of the present invention can improve
focusing accuracy when reliability of a focusing result in a main
focus adjustment area is low due to low illuminance or low contrast
of a main object.
[0016] Further features and aspects of the present invention will
become apparent from the following detailed description of
exemplary embodiments with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate exemplary
embodiments, features, and aspects of the invention and, together
with the description, serve to explain the principles of the
invention.
[0018] FIG. 1 is a block diagram illustrating an example
configuration of an electronic camera according to an exemplary
embodiment of the present invention.
[0019] FIG. 2 is a flowchart illustrating focusing control
according to a first exemplary embodiment of the present
invention.
[0020] FIGS. 3A and 3B illustrate example methods for setting a
focus adjustment area according to the first exemplary embodiment
of the present invention.
[0021] FIG. 4 is a flowchart illustrating focusing determination
processing according to the first exemplary embodiment of the
present invention.
[0022] FIG. 5 is a flowchart illustrating a checking procedure of
monotonic decrease in an infinite distance end direction performed
in step S34 in FIG. 4.
[0023] FIG. 6 is a flowchart illustrating a checking procedure of
monotonic decrease in a minimum object distance end direction
performed in step S36 in FIG. 4.
[0024] FIG. 7 illustrates the relationship between a focus lens
position and a focus evaluation value when focusing is
available.
[0025] FIG. 8 is a flowchart illustrating focusing control
according to a second exemplary embodiment of the present
invention.
[0026] FIG. 9 illustrates a method for setting focus adjustment
areas according to the second exemplary embodiment of the present
invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0027] Various exemplary embodiments, features, and aspects of the
invention will be described in detail below with reference to the
drawings.
First Exemplary Embodiment
[0028] FIG. 1 is a block diagram illustrating a configuration of an
electronic camera according to the first exemplary embodiment of
the present invention.
[0029] The electronic camera includes a photographic lens 101
including a zoom mechanism, a diaphragm and shutter 102 configured
to control the amount of light, an automatic exposure (AE)
processing unit 103, a focus lens 104 movable to perform focusing
on an image sensor 108, an automatic focus (AF) processing unit
105, a flash unit 106, a flash (EF) processing unit 107, and the
image sensor 108 configured to convert incident light into an
electrical signal.
[0030] The electronic camera further includes an analog-to-digital
(A/D) converter 109 including a correlated double sampling (CDS)
circuit configured to eliminate an output noise from the image
sensor 108 and a nonlinear amplifying circuit operable before A/D
conversion, an image processing unit 110, a white balance (WB)
processing unit 111, and a format converter 112. A high-speed
built-in memory 113 is, for example, a random access memory
(hereinafter referred to as DRAM) used as a high-speed buffer
functioning as a temporary image storing unit or an operation
memory in compressing and expanding an image. An image recording
unit 114 includes a recording medium, such as a memory card, and an
interface of the recording medium.
[0031] The electronic camera further includes a system control unit
115 configured to control the electronic camera, for example, to
control an imaging sequence, an image display memory 116
(hereinafter referred to as VRAM), and an operation display unit
117 configured to display an image, an operation guidance, a camera
state, and a focus adjustment area on a photographing screen at the
time of photographing. An operation unit 118 is operable to
externally operate the camera. The operation unit 118 includes, for
example, a menu switch operable to perform various types of
setting, e.g., setting of a photographing function of the
electronic camera and setting at the time of reproducing an image,
a zoom lever operable to instruct a zoom operation of the
photographic lens 101, and an operation mode changeover switch
operable to switch a photographing mode and a reproduction mode.
The electronic camera further includes a photographic mode switch
(SW) 119 operable to set a mode of photographing, a main switch 120
operable to supply power to the electronic camera, a switch 121
(hereinafter referred to as SW1) operable to instruct a
photographing standby operation, such as auto-focus (AF) or
auto-exposure (AE), and a photographing switch 122 (hereinafter
referred to as SW2) operable to instruct photographing after
operating the SW1 121.
[0032] Then, a focusing control operation of the electronic camera
having the above-described configuration according to the present
embodiment will be described in detail below with reference to
FIGS. 2 to 7. The system control unit 115 performs the focusing
control operation in cooperation with the image processing unit
110.
[0033] FIG. 2 is a flowchart illustrating a focusing control
procedure according to the present embodiment, and FIGS. 3A and 3B
illustrate focus adjustment areas in the focusing control.
[0034] Referring to FIG. 2, when focusing control starts, the
processing proceeds to step S11. In step S11, the system control
unit 115 sets a frame (hereinafter referred to as a main frame)
indicating a focus adjustment area (a main area) which can be
considered to include a main object therein, and then the
processing proceeds to step S12. The position and size of the main
frame can be the center of a screen and an arbitrary size, a
position and size determined based on a detected result of the main
object using a face detection method or a moving object detection
method, or a position and size arbitrarily instructed by a
user.
[0035] In step S12, the system control unit 115 sets frames
(hereinafter referred to as subframes) indicating a plurality of
focus adjustment areas (subareas) around the main frame, and then
the processing proceeds to step S13. The number of plural subframes
is A.times.B (A and B are arbitrary integers) including the main
frame (illustrated with a thick frame) and the size thereof is the
same as that of the main frame, as illustrated in FIG. 3A (the
number is 5.times.3 in FIG. 3A). The number, size, and position of
subframes are not limited to those illustrated in FIG. 3A. In step
S13, the system control unit 115 loads images from the focus
adjustment areas (the main frame and the subframes), which are set
in step S11 and step S12, while moving the focus lens 104. Then,
the system control unit 115 performs AF scanning to acquire a
contrast value (or a focus evaluation value) indicating a focusing
state of each focus adjustment area, and then the processing
proceeds to step S14.
[0036] In step S14, the system control unit 115 acquires a peak
position of the focus lens 104 having a maximum focus evaluation
value acquired in step S13, i.e., an in-focus point, for every
focus adjustment area by calculation, and then the processing
proceeds to step S15. In step S15, the system control unit 115
selects a subframe or subframes having a peak position at a depth
of within .+-..alpha. (within a predetermined range), which is a
predetermined range previously set with respect to a peak position
of the main frame, and then the processing proceeds to step S16.
Since the subframe or subframes selected in step S15 (the number of
selected subframes is M) are an area in which the main object
presumably exists, the system control unit 115 uses peak positions
(AF results) of the selected subframes if the reliability of a
calculated peak position (AF result) of the main frame is low. FIG.
3B illustrates a case where three subframes (that is, M=3)
including an object having the approximately same distance as the
main object in the main frame are selected by AF result.
[0037] In step S16, the system control unit 115 initializes a
variable i indicating a frame whose AF result is to be used, and
then the processing proceeds to step S17. In step S17, the system
control unit 115 determines whether focusing is available based on
the AF result of the main frame. If focusing is available (YES in
step S17), the processing proceeds to step S18. In step S18, the
system control unit 115 drives the focus lens 104 to a peak
position of the main frame, and then the processing proceeds to
step S19. If focusing is not available (NO in step S17), the
processing proceeds to step S20. A method for determining whether
focusing is available in step S17 will be described in detail below
with reference to FIGS. 4 to 7.
[0038] In step S20, the system control unit 115 increments the
variable i, which indicates a frame whose AF result is to be used,
and then the processing proceeds to step S21. In step S21, the
system control unit 115 determines whether a subframe whose AF
result can be used exists, that is, whether the number M of
subframes selected in step S15 is equal to or greater than the
variable i. If a subframe whose AF result can be used exists (YES
in step S21), the processing proceeds to step S22. If no subframe
whose AF result can be used exists (NO in step S21), the processing
proceeds to step S27. In step S22, the system control unit 115
calculates an addition average of an AF result of a subframe having
a peak position i-th nearest to a peak position of the main frame
among the subframes selected in step S15, and then the processing
proceeds to step S23.
[0039] More specifically, addition average is performed as follows.
In AF scanning performed in step S13, positions of the focus lens
104 are a, b, c, d, . . . , and focus evaluation values of the main
frame at the respective positions of the focus lens 104 are P(a),
P(b), P(c), P(d) . . . . Further, focus evaluation values of the
subframe having a peak position i-th nearest to the peak position
of the main frame are Qi (a), Qi (b), Qi (c), Qi (d) . . . . The AF
results after addition average A(a), A(b), A(c), A(d), . . . , are
as follows:
A ( a ) = [ P ( a ) + Qi ( a ) ] ( i + 1 ) ##EQU00001## A ( b ) = [
P ( b ) + Qi ( b ) ] ( i + 1 ) ##EQU00001.2## A ( c ) = [ P ( c ) +
Qi ( c ) ] ( i + 1 ) ##EQU00001.3## A ( d ) = [ P ( d ) + Qi ( d )
] ( i + 1 ) ##EQU00001.4##
[0040] In step S23, the system control unit 115 determines whether
focusing is available based on AF results after addition average
A(a), A(b), A(c), A(d) . . . . If focusing is available (YES in
step S23), the processing proceeds to step S24. If focusing is not
available (NO in step S23), the processing proceeds to step S20.
Determination of focusing in step S23 is performed by a similar
method to that in step S17, which will be described below with
reference to FIGS. 4 to 7. In step S24, the system control unit 115
calculates a peak position based on the AF results after addition
average A(a), A(b), A(c), A(d), . . . , and then the processing
proceeds to step S25. In step S25, the system control unit 115
determines whether a difference between the peak position of the
main frame and the peak position after addition average is greater
than a depth .beta.. If the difference is greater than the depth
.beta. (YES in step S25), the processing proceeds to step S18. If
the difference is not greater than the depth .beta. (NO in step
S25), the processing proceeds to step S26. In step S26, the system
control unit 115 drives the focus lens 104 to the peak position
after addition average, and then the processing proceeds to step
S19.
[0041] In step S19, the system control unit 115 displays an
in-focus state, and then focusing control ends. The system control
unit 115 can display only the main frame as an in-focus display
frame. However, when subframes used for addition average exist, the
system control unit 115 can display all of the frames used for
addition average as in-focus display areas.
[0042] In step S27, since focusing control using a focus evaluation
values is not available, the system control unit 115 drives the
focus lens 104 to a predetermined position or the peak position of
the main frame, and then the processing proceeds to step S28. In
step S28, the system control unit 115 displays an out-of-focus
state, and then focusing control ends.
[0043] Now, a method for determining whether focusing is available
in steps S17 and S23 will be described in detail below with
reference to FIGS. 4 to 7. This determination is performed
according to whether a focus evaluation value satisfies a
predetermined condition.
[0044] When a focus evaluation value is shown with a graph having a
focus lens position at the abscissa axis and a focus evaluation
value at the ordinate axis, the shape is a hill shape as
illustrated in FIG. 7, except specific cases, such as a conflict
between far and near objects. Therefore, the system control unit
115 can perform focusing determination by determining whether a
focus evaluation value has a hill shape based on a difference
between a maximum value and a minimum value of the focus evaluation
value, the length of a part inclining with a inclination equal to
or greater than a predetermined value (SlopeThr), and the slope of
an inclining part. The result of the focusing determination is
output with 0 or 1 as illustrated below. [0045] 0: Focus adjustment
of an object is available based on a peak position of the focus
evaluation value. [0046] 1: Contrast of an object is insufficient
or an object is located at a distance outside a scanned distance
range.
[0047] As illustrated in FIG. 7, points up to which inclination is
continued from a hill top (point A) are denoted as point D and
point E, the width between point D and point E is denoted as a
width L of the hill, a difference between a focus evaluation values
at point A and point D is denoted as SL1, a difference between the
focus evaluation values at point A and point E is denoted as SL2,
and the sum of SL1 and SL2 is denoted as SL. Points B and C each
indicate a point at which the focus evaluation value has decreased
by a predetermined value SlopeThr with respect to point A.
[0048] FIG. 4 is a flowchart of a method for determining whether
focusing is available, which is performed in steps S17 and S23 in
the flowchart of FIG. 2.
[0049] In step S31, the system control unit 115 acquires a focus
evaluation maximum value, minimum value, and a focus lens 104
position io (a scan point) giving the maximum value. In step S32,
the system control unit 115 initializes variables L and SL to 0,
where L indicates a width of the hill of a focus evaluation value
and SL indicates a slope of the hill. In step S33, the system
control unit 115 determines whether the scan point io giving the
maximum value is an infinite distance end position in a scanned
predetermined area. If the scan point io is not the infinite
distance end position (NO in step S34), the processing proceeds to
step S34. In step S34, the system control unit 115 checks a
monotonic decrease in an infinite distance end direction. If the
scan point io is the infinite distance end position (YES in step
S34), the processing skips step S34 and then proceeds to step
S35.
[0050] Here, processing for checking a monotonic decrease in the
infinite distance end direction in step S34 will be described below
with reference to the flowchart of FIG. 5.
[0051] In step S51, the system control unit 115 initializes a
counter variable i to io. In step S52, the system control unit 115
compares a difference between a value d[i] of a focus evaluation
value in a scan point i and a value d[i-1] of a focus evaluation
value in a scan point i-1 with a predetermined value SlopeThr. The
scan point i-1 is nearer to the infinite distance end side by one
scan point than the scan point i. If the relation is not
d[i]-d[i-1] >SlopeThr (NO in step S52), the system control unit
115 determines that a monotonic decrease in the infinite distance
end direction does not occur. Then, the processing for checking a
monotonic decrease in the infinite distance end direction ends.
Then, the processing proceeds to step S35 in FIG. 4.
[0052] If the relation is d[i]-d[i-1].gtoreq.SlopeThr (YES in step
S52), the system control unit 115 determines that a monotonic
decrease in the infinite distance end direction occurs, and then
the processing proceeds to step S53. In step S53, the system
control unit 115 updates the variable L indicating the length of a
part (a width of hill) where the focus evaluation value inclines
with a inclination equal to or greater than a predetermined value,
and the variable SL indicating an amount of decrease in a monotonic
decrease range according the following formulae:
L=L+1
SL=SL+(d[i]-d[i-1])
[0053] In step S54, the system control unit 115 decrements the
counter variable i as i=i-1 to shift a point to be detected by one
scan point towards the infinite distance end side. In step S55, the
system control unit 115 checks whether the counter variable i has
become a value at the infinite distance end position (=0) in a
scanned predetermined area. If the value of the counter variable i
is 0, that is, if the start point to detect a monotonic decrease
reaches the infinite distance end position in the scanned
predetermined area (YES in step S55), the processing for checking a
monotonic decrease in the infinite distance end direction ends.
Then, the processing proceeds to step S35. If the value of the
counter variable i is not 0 (NO in step S55), the processing
returns to step S52.
[0054] As described above, the system control unit 115 checks a
monotonic decrease in the infinite distance end direction from
i=io.
[0055] Referring back to FIG. 4, in step S35, the system control
unit 115 determines whether the scan point io giving the maximum
value of the focus evaluation value is a minimum object distance
end position in the scanned predetermined area. If the scan point
io is not the minimum object distance end position (NO in step
S35), the processing proceeds to step S36. In step S36, the system
control unit 115 checks a monotonic decrease in the minimum object
distance end direction. If the scan point io is the minimum object
distance end position (YES in step S35), the processing skips step
S36 and then proceeds to step S37.
[0056] Here, the processing for checking a monotonic decrease in
the minimum object distance end direction in step S36 will be
described below with reference to FIG. 6.
[0057] In step S61, the system control unit 115 initializes the
counter variable i to io. In step S62, the system control unit 115
compares a difference between a value d[i] of a focus evaluation
value in a scan point i and a value d[i+1] of a focus evaluation
value in a scan point i+1 with a predetermined value SlopeThr. The
scan point i+1 is nearer to the minimum object distance end side by
one scan point than the scan point i. If the relation is not
d[i]-d[i+1].gtoreq.SlopeThr (NO in step S62), the system control
unit 115 determines that a monotonic decrease in the minimum object
distance end direction does not occur. Then, the processing for
checking a monotonic decrease in the minimum object distance end
direction ends. Then, the processing proceeds to step S37 in FIG.
4.
[0058] On the other hand, if the relation is
d[i]-d[i+1].gtoreq.SlopeThr (YES in step S62), the system control
unit 115 determines that a monotonic decrease in the minimum object
distance end direction occurs. Then, the processing proceeds to
step S63. In step S63, the system control unit 115 updates the
variable L indicating the length of a part (a width of hill) where
the focus evaluation value inclines with a inclination equal to or
greater than a predetermined value, and the variable SL indicating
an amount of decrease in a monotonic decrease range according the
following formulae:
L=L+1
SL=SL+(d[i]-d[i+1])
[0059] In step S64, the system control unit 115 increments the
counter variable i as i=i+1 to shift a point to be detected by one
scan point towards the minimum object distance end side. In step
S65, the system control unit 115 checks whether the counter
variable i has become a value (=N) at the minimum object distance
end position in a scanned predetermined range. If the value of the
counter variable i reaches N, that is, the start point to detect a
monotonic decrease reaches the minimum object distance end position
in the scanned predetermined range (YES in step S65), the
processing for checking a monotonic decrease in the minimum object
distance end direction ends. Then, the processing proceeds to step
S37. If the value of the counter variable i is not N (NO in step
S65), the processing returns to step S52.
[0060] As described above, the system control unit 115 checks a
monotonic decrease in the minimum object distance end direction
from i=io.
[0061] When the processing for checking a monotonic decrease in the
infinite distance end direction and the minimum object distance end
direction ends, the system control unit 115 compares each
coefficient with a threshold value to check whether the calculated
focus evaluation value has a hill shape, and determines whether
focusing is available.
[0062] In step S37, the system control unit 115 determines whether
the following two conditions are simultaneously satisfied. That is,
the system control unit 115 determines whether the scan point io
giving the maximum value of the focus evaluation value is the
minimum object distance end position in the scanned predetermined
range. Further, the system control unit 115 determines whether a
difference between the value d[n] of a focus evaluation value in a
scan point n and a value d[n-1] of a focus evaluation value in a
scan point n-1 is equal to or greater than the predetermined value
SlopeThr. The scan point n-1 is nearer to the infinite distance end
side by one scan point than the san point n. If the scan point io
is the minimum object distance end position and the difference is
equal to or greater than the predetermined value SlopeThr (YES in
step S37), the processing proceeds to step S41. If not both of
these conditions are satisfied (NO in step S37), the processing
proceeds to step S38.
[0063] In step S38, the system control unit 115 determines whether
the following two conditions are simultaneously satisfied. That is,
the system control unit 115 determines whether the scan point io
giving the maximum value of the focus evaluation value is the
infinite distance end position in the scanned predetermined range.
Further, the system control unit 115 determines whether a
difference between the value d[0] of a focus evaluation value in
the scan point 0 and a value d[1] of a focus evaluation value in
the scan point 1 is equal to or greater than the predetermined
value SlopeThr. The san point 1 is nearer to the minimum object
distance end side by one scan point than the san point 0. If the
scan point io is the infinite distance end position and the
difference is equal to or greater than the predetermined value
SlopeThr (YES in step S38), the processing proceeds to step S41. If
not both of these conditions are satisfied (NO in step S38), the
processing proceeds to step S39.
[0064] In step S39, the system control unit 115 determines whether
the following three conditions are simultaneously satisfied. The
system control unit 115 determines whether the length of a part L
inclining with a inclination equal to or greater than a
predetermined value is equal to or greater than a predetermined
value L0. Further, the system control unit 115 determines whether
an average value SL/L of the inclining part is equal to or greater
than a predetermined value SL0/L0. Furthermore, the system control
unit 115 determines whether the difference between a maximum value
and a minimum value of the focus evaluation value is equal to or
greater than a predetermined value. If the length L is equal to or
greater than the predetermined value L0, the average value SL/L is
equal to or greater than the predetermined value SL0/L0, and the
difference between the maximum value and the minimum value of the
focus evaluation value is equal to or greater than the
predetermined value (YES in step S39), the processing proceeds to
step S40. If not all of these conditions are satisfied (NO in step
S39), the processing proceeds to step S41. In step S40, the system
control unit 115 sets a determined result to 0 since the calculated
focus evaluation value has a hill shape and focus adjustment of an
object is available. On the other hand, in step S41, the system
control unit 115 sets a determined result to 1 since the calculated
focus evaluation value does not have a hill shape and focus
adjustment of an object is not available.
[0065] As described above, the system control unit 115 performs a
determination as to whether focusing is available.
[0066] According to the above-described exemplary embodiment, when
focusing is not available based only a focus evaluation value in a
main focus adjustment area, the system control unit 115 performs
focusing control using a focus adjustment subarea or subareas
having an object in an approximately same distance around the main
focus adjustment area. As a result, there is no problem such as
missing of a background, a focus adjustment area can be expanded,
and the S/N ratio can be improved. Thus, focusing accuracy can be
improved.
[0067] In addition, when reliability of a focus evaluation value of
a main frame is low, AF results of focus evaluation values of
plural subframes around the main frame can be used only in the case
of a dark condition.
Second Exemplary Embodiment
[0068] A second exemplary embodiment of the present invention will
be described below.
[0069] The first exemplary embodiment improves reliability of a
focusing result of a main frame by adding focus adjustment areas
around the main frame. On the other hand, the second exemplary
embodiment uses another focusing control method to improve
reliability of an AF result of a main frame.
[0070] FIG. 8 is a flowchart illustrating focusing control
according to the second exemplary embodiment. FIG. 9 illustrates
focus adjustment areas according to the second exemplary embodiment
of the present invention.
[0071] In the present embodiment, when focusing control starts, the
processing proceeds to step S101. In step S101, the system control
unit 115 sets a main frame. Similar to the first exemplary
embodiment, the position and size of the main frame can be a screen
center and an arbitrary size, a position and size determined based
on a detected result of the main object using a face detection
method a moving object detection method, or a position and size
arbitrarily instructed by a user. In step S102, the system control
unit 115 sets a plurality of focus adjustment areas (hereinafter
referred to as subframes) having different sizes and internally
including the main frame at a center thereof, and then the
processing proceeds to step S103. The number of set subframes is M.
For example, as illustrated in FIG. 9, the system control unit 115
sets the subframes, such as a frame W1, a frame W2, and a frame W3,
to include a main frame (W0) at a center thereof. FIG. 9
illustrates a case where M is 3.
[0072] In step S103, the system control unit 115 performs AF
scanning, and then the processing proceeds to step S104. In AF
scanning, the system control unit 115 loads images from focus
adjustment areas (including the main frame and the subframes),
which are set in step S101 and step S102, while driving the focus
lens 104, and acquires a contrast value (focus evaluation value) of
each focus adjustment area.
[0073] In step S104, the system control unit 115 calculates a peak
position of the focus lens 104 at which the focus evaluation value
acquired in step S103 becomes maximum, and then the processing
proceeds to step S105. In step S105, the system control unit 115
initializes a variable i indicating the order of size of a focus
adjustment area to 0, and then the processing proceeds to step
S106.
[0074] In step S106, the system control unit 115 determines whether
focusing is available based on an AF result of the main frame (W0).
If focusing is available (YES in step S106), the processing
proceeds to step S107. If focusing is not available (NO in step
S106), the processing proceeds to step S109. In addition, the
system control unit 115 determines whether focusing is available by
a similar method described with reference to FIGS. 4 to 7 in the
first exemplary embodiment. In step S107, the system control unit
115 drives the focus lens 104 to a peak position of the main frame
(W0), and then the processing proceeds to step S108. In step S108,
the system control unit 115 displays an in-focus state. Then, the
focusing control processing ends.
[0075] In step S109, the system control unit 115 increments the
variable i, indicating the order of size of a subframe, and then
the processing proceeds to step S110. In step S110, the system
control unit 115 determines whether the i-th largest focus
adjustment area (frame Wi) except the main frame exists, that is,
whether i is equal to or less than M. If the i-th largest focus
adjustment area exists (YES in step S110), the processing proceeds
to step S111. If the i-th largest focus adjustment area does not
exist (NO in step S110), the processing proceeds to step S113.
[0076] In step S111, the system control unit 115 determines whether
focusing is available based on an AF result of the frame Wi, as
described with reference to FIGS. 4 to 7. If focusing is available
(YES in step S111), the processing proceeds to step S112. If
focusing is not available (NO in step S111), the processing returns
to step S109. In step S109, the system control unit 115 repeats the
above-described processing.
[0077] In step S112, the system control unit 115 checks whether the
difference between a peak position of the main frame (W0) and a
peak position of the frame Wi is greater than a depth .beta.. If
the difference is greater than the depth .beta. (YES in step S112),
the processing proceeds to step S113. If the difference is not
greater than the depth .beta. (NO in step S112), the processing
proceeds to step S107. In step S107, the system control unit 115
drives the focus lens 104 to the peak position of the frame Wi, and
then the processing proceeds to step S108. In step S108, the system
control unit 115 displays an in-focus state. Then, the focusing
control ends. In addition, an in-focus display frame can be the
main frame or the frame Wi.
[0078] In step S113, the system control unit 115 drives the focus
lens 104 to a predetermined position or the peak position of the
main frame, and then the processing proceeds to step S114. In step
S114, the system control unit 115 displays an out-of-focus state.
Then, the focusing control ends.
[0079] According to the above-described second exemplary
embodiment, when focusing is not available based only a focus
evaluation value in a main focus adjustment area, the system
control unit 115 performs focusing control using a main focus
adjustment area and a focus adjustment subarea or subareas
including an area around the main focus adjustment area. As a
result, there is no problem such as missing of a background, a
focus adjustment area can be expanded, and the S/N ratio can be
improved. Thus, focusing accuracy can be improved.
[0080] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all modifications, equivalent
structures, and functions. This application claims priority from
Japanese Patent Application No. 2007-240183 filed Sep. 14, 2007,
which is hereby incorporated by reference herein in its
entirety.
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